1. Field of the Invention
The present invention is generally related to injection of water into an exhaust system and, more particularly, a method by which a micro-processor controls the injection of predetermined amounts of water into an exhaust system based one or more conditions relating to the operation of the internal combustion engine.
2. Description of the Prior Art
It is well know that certain operational advantages can be achieved by injecting water into the exhaust system of an internal combustion engine. This concept is described in detail in U.S. Pat. No. 3,385,052, which issued to Holterman et al on May 28, 1968. The exhaust system described is operated according to a method which comprises the steps of discharging burned gases from a combustion chamber through an exhaust port to an exhaust passage in order to obtain timed return of a pressure wave to the exhaust port by injecting a liquid into the burned gases discharged from the combustion chamber. Also disclosed is an internal combustion engine having a means for timing the return to an exhaust port of a pressure wave in an exhaust passageway, including means for supplying a cooling liquid to the passageway. The engine includes an exhaust passageway which increases an internal cross section in the direction away from the exhaust port and terminates in a wall that is transversed to that direction. The passageway also includes a means for defining an opening which is located adjacent to the wall and which has a relatively small area as compared to the area of the wall.
U.S. Pat. No. 3,813,880, which issued to Reid et al on Jun. 4, 1974, discloses an exhaust tuning system for a two stroke engine. The engine includes a pair of exhaust chambers having a common control wall and each of which is connected between a corresponding plurality of selected cylinders and a common exhaust passageway. The connection between each of the chambers and the passageway is defined by a tuning section which is constructed of sufficient length and a configuration to generate a negative pressure pulse to aid scavenging and reflected positive pulses from the fired cylinder. In addition, the next fired cylinder of each group establishes a super-charging of the engine. The common wall between the two tuned passageways is provided with a transfer port for transferring of a positive pressure signal from the one passageway into the opposite passageway which travels back toward the engine to provide a further positive super-charging pulse to the opposite exhaust chamber. The feedback pressure wave can be applied with a particular advantage to four and two cylinder engines.
U.S. Pat. No. 5,746,054, which issued to Matte on May 5, 1998, describes a method and apparatus for a tuned pipe water injection. In an exhaust expansion chamber or tuned pipe of a two-cycle engine in a watercraft, variable amounts of water are injected, thus cooling the temperature within the expansion chamber and matching the sonic wave speed with that of the correct rpm of the motor. Thus, by regulating the temperature of the exhaust gases in the tuned pipe with water, the efficiency of the two-cycle engine at varying revolutions per minute is improved.
U.S. Pat. No. 4,014,282, which issued to Kollman on Mar. 29, 1977, discloses an exhaust tube mounting apparatus for outboard motors. In an outboard motor, the engine exhausts through the drive shaft housing in which an exhaust tube directs the gases into a lower propeller unit secured to the housing. The exhaust tube has support legs on the opposite top sides. Bushings encircle each lug and they rest in receptacles on the upper interior portions of the housing. An adapter plate is secured to the housing, clamps the lugs in place and moves the lower end of the tube into sealing relationship within a lower bushing within the housing. The lower bushing is a rubber-like annular bushing having a projecting ledge aligned with the lower end of the exhaust tube. The inner wall of the bushing has an inwardly and downwardly extended lop deflected and sealing with the side of the exhaust tube.
U.S. Pat. No. 3,808,807, which issued to Lanpheer on May 7, 1974, discloses a tuning arrangement for an outboard motor. The improvement in the exhaust system for a two cycle engine comprises one or more sets of three cylinders connected to the crankshaft 120.degree. apart, the exhaust ports of which communicate with a common exhaust chamber formed in association with the cylinder block. A diverging passage leading from the common exhaust chamber to a spacious exhaust tube enclosed within the drive shaft housing produces a negative pressure from the cylinder's positive exhaust pulse, which negative pressure aids in scavenging the cylinder. The geometry of the diverging passage and the exhaust tube are such that a positive pulse is created by the exit of the negative pulse from said diverging passage and propagates back through the diverging passages arriving at the exhaust ports of the cylinder simultaneously with a positive pulse from a subsequently fired cylinder to aid in supercharging.
U.S. Pat. No. 4,920,745, which issued to Gilbert on May 1, 1990, describes an internal combustion engine which has a transfer port and an exhaust port in a cylinder which are opened and closed in a timed relationship by the reciprocating movement of a piston. The exhaust port communicates with an exhaust passage that is tuned to provide a pressure pattern in the exhaust passageway that will create at the exhaust port a predetermined pressure pattern while the exhaust port is opened. Coolant is supplied to the exhaust passage when the engine is subject to increasing transient load conditions, at engine speed below the tuned speed, and at a controlled rate to establish a tuned state in the exhaust passage during the transient condition.
U.S. Pat. No. 5,378,180, which issued to Nakayama et al on Jan. 3, 1995, describes an exhaust system for outboard motors which have exhaust pipes and expansion chambers into which the exhaust pipes extend. A catalyst is positioned in the exhaust system downstream of the point where the exhaust pipe terminates in the expansion chamber so as to preclude interference with the exhaust timing. The catalyst bed is removable for ease of servicing without necessitating removal of the outboard motor from its attachment to the associated watercraft and a trap device is provided for precluding water from entering the engine through its exhaust ports.
All of the patents described above are hereby expressly incorporated in the following description.
As described above, it is well known that exhaust systems can be tuned to advantageously time the arrival of reflected pressure waves at the exhaust port of a cylinder. This is done for several reasons which are all well known to those skilled in the art. Proper tuning of the exhaust system can produce super charging within the combustion chambers of the engine. These techniques are also advantageous in preventing certain quantities of unburned hydrocarbons from being exhausted through the exhaust ports following a combustion event within the combustion chamber. The advantageous effect of this procedure is obtained by changing the temperature of the exhaust gases. The speed of sound is affected by the temperature within the exhaust system and, as a result, the effective length of the exhaust pipe is changed by changing the speed at which the pressure pulses move within the exhaust pipe. By cooling the exhaust gases, the speed of the pressure pulses is slowed. This has the effect of increasing the effective length of the exhaust pipe. At different speeds of engine operation, it would be theoretically advantageous to actually have different lengths of exhaust pipe. This being impractical, it has been discovered that changes in temperature of the exhaust gases has the same affect as dynamically changing the length of the exhaust pipe.
In the prior art, many different techniques have been applied to control the rate at which water is injected into the exhaust pipe for these purposes of changing the speed of sound within the exhaust system. Certain mechanical systems, such as pressure responsive valves, have been used to change the rate at which water is injected into the exhaust system as a function of engine condition.
It would be significantly advantageous if a system could be developed in which the amount of water injected into an exhaust system could be accurately controlled, not only as a function of engine speed and/or throttle position, but also as a function of the natural operating characteristics of the engine. In other words, certain engines require different amounts of injected water at various speeds than other engines do at those same speeds. In addition, different lengths of exhaust pipes are used with different engines and, therefore, the rate of water injection into the exhaust system is a function of engine speed and/or throttle position is different for each engine type and exhaust pipe length.